Low-frequency tuning-fork electromechanical filter



p 26, 1967 KENJI TAKAHASHI 3,344,367

LOW-FREQUENCY TUNING-FORK ELECTROMECHANI CAL FILTER Filed Dec. 17. 19.65

United States Patent 3,344,367 LOW-FREQUENCY TUNING-FORK ELECTROMECHANICAL FILTER Kenji Takahashi, Tokyo-t0, Japan, assignor to Kokusai Denki Kabushiki Kaisha (also known as Kokusai Electric Co., Ltd.), Tokyo-to, Japan, a joint-stock company of Japan Filed Dec. 17, 1965, Ser. No. 514,518 Claims'priority, application Japan, Dec. 30, 1964, 39/ 74,501 3 Claims. (Cl. 333-71) ABSTRACT OF THE DISCLOSURE A multiple tuning-fork electromechanical filter with bifurcated couplers serially coupling the tuning-fork resonators, the legs of the resonators and couplers being in parallel to avoid torsional moments therebetween during transmission of mechanical vibrations.

This invention relates to electromechanical wave filters and more particularly to improvements in or relating to electromechanical filters for low frequencies.

In general, tuning forks or tuning bars are used as mechanical resonators for low frequencies. It is well known that a low-frequency electromechanical filter is composed of these mechanical resonators and transducers, electrostrictive ceramics secured to the resonators at the two ends, and couplers intercoupling the mechanical resonators.

It is an object of the present invention to afford miniaturization of filters of the instant type by improving the mechanical couplers intercoupling the mechanical resonators.

Another object of the invention is to facilitate the variation of bandwidth of the mechanical filters.

A further object of the invention is to facilitate the fabrication of the mechanical filters.

According to the present invention, briefly stated, there is provided a low-frequency electromechanical filter having tuning forks or tuning bars as resonators, characterised in that the resonators are intercoupled by bifurcated couplers.

The nature, principle, and the details of the invention will be more clearly apparent from the following detailed description with respect to a preferred embodiment of the invention, when read in conjunction with the accompanying drawing in which like parts are designated by like reference numerals, and in which:

FIGURE 1 is a schematic diagram indicating the essential composition and arrangement of the embodiment of the invention; and

FIGURE 2 is an enlarged perspective view showing an essential part of the filter according to the invention.

Referring to FIGURE 1, the filter diagrammatically illustrated therein is provided with input and output terminals 1 and 2 provided with matching coils 3, which are inserted for conjugate matching for the purpose of accomplishing electromechanical transduction by means of electrostrictive ceramic elements. The filter further comprises tuning fork resonators 4, transducer resonators 5 in successive arrangement electrostrictive ceramic eleice ments 6 secured to the end transducer resonators 5 and couplers 7 intercoupling adjacent resonators 4 and 5.

According to the present invention, each coupler has a bifurcated shape, which is of U-shape or the shape of a tuning fork in the example illustrated, so as to undergo tuning fork vibration (or bending vibration). In contrast, conventional couplers are of bar shape, and, while their longitudinal or torsional vibrating coupling affords intercoupling of the resonators, the use of bar-shaped couplers in the case of low frequencies of the order of 400 c./ s. to 3 k-c./s. necessitates very long couplers in order to obtain the desired bandwidth. Consequently, bar-shaped couplers are disadvantageous for low frequencies in that the filter unavoidably becomes large in size.

When the coupler is provided with a bifurcated shape, its physical size becomes a fraction of that of the resonators, and the gap between its opposed vibration prongs can be made substantially small without greatly affecting the vibration characteristics. Accordingly, the coupler can be made small and compact.

Furthermore, by attaching the couplers in the direction of propagation of the bending vibration energy, that is, parallelly to the resonators as shown in the drawing, coupling due to torsional moment is eliminated, and the coupling becomes that due to only bending vibration. Accordingly, the design and fabrication of the filter are greatly facilitated.

In addition, since the filter bandwidth is related to the mass of the resonators, the dimensions of the couplers, and the vibration amplitude at the coupling points, fractional bandwidths can be readily varied from 0.1 to 20 percent, of course, by changing the thickness and length of each coupler and the points of coupling to the resonators. In this respect, a U-shaped coupler is advantageous in that its length can be increased without increasing the length of the entire filter.

In attaching the couplers to the resonators, the couplers may be held in aligned position and secured to the resonators at points 8 as shown in FIGURE 2 by welding, soldering, brazing, or like method, which attachment process is extremely simple.

While the above description and drawing relate particularly to a U-shaped coupler, similar desirable results can, of course, be obtained by the use of a modification of the U-shape such as, for example, a V-shape.

Accordingly, it should be understood that the foregoing disclosure relates to only a preferred embodiment of the invention and that it is intended to cover all changes and modifications of the example of the invention herein chosen for the purposes of the disclosure which do not constitute departures from the spirit and scope of the invention as set forth in the appended claims.

What I claim is:

1. A low-frequency electromechanical filter comprising, a plurality of tuning-fork resonators, a plurality of bifurcated mechanical couplers serially, continuously coupling next adjacent ones of said resonators, said couplers each comprising a bifurcated resonator having legs each continuously, mechanically connected to a respective leg of a pair of the next adjacent tuning-fork resonators, said couplers being disposed for transmitting in operation mechanical vibrations serially through said tuning-fork resonators, means comprising electromechanical transducers coupled to opposite end tuning-fork resonators of said filter for receiving at one end of said filter an electrical input to be filtered and converting into mechanical vibrations and converting said mechanical vibrations for taking out at an opposite end of said filter a filtered electrical output.

2. A low-frequency electromechanical filter according to claim 1, in which the legs of said resonators and the legs of the respective couplers are disposed parallel thereby to avoid torsional moments therebetween during propagation of said mechanical vibration-s.

3. A low-frequency electromechanical filter according 4 to claim 1, in which the legs of said couplers and the legs of the resonators coupled thereby are relatively disposed to effectively avoid torsional moments therebetween during propagation of said mechanical vibrations.

References Cited UNITED STATES PATENTS 2,152,955 4/1939 Coyne 33371 10 ROY LAKE, Primary Examiner.

DARWIN R. HOSTETTER, Examiner. 

1. A LOW-FREQUENCY ELECTROMECHANICAL FILTER COMPRISING, A PLURALITY OF TUNING-FORK RESONATORS, A PLURALITY OF BIFURCATED MECHANICAL COUPLERS SERIALLY, CONTINUOUSLY COUPLING NEXT ADJACENT ONES OF SAID RESONATORS, SAID COUPLERS EACH COMPRISING A BIFURCATED RESONATOR HAVING LEGS EACH CONTINUOUSLY, MECHANICALLY CONNECTED TO A RESPECTIVE LEG OF A PAIR OF THE NEXT ADJACENT TUNING-FORK RESONATORS, SAID COUPLERS BEING DISPOSED FOR TRANSMITTING IN OPERATION MECHANICAL VIBRATIONS SERIALLY THROUGH SAID TUNING-FORK RESSONATORS, MEANS COMPRISING ELECTROMECHANICAL TRANSDUCERS COUPLED TO OPPOSITE END TUNING-FORK RESONATORS OF SAID FILTER FOR RECEIVING AT ONE END OF SAID FILTER AN ELECTRICAL INPUT TO BE FILTERED AND CONVERTING INTO MECHANICAL VIBRATIONS AND CONVERTING SAID MECHANICAL VIBRATIONS FOR TAKING OUT AT AN OPPOSITE END OF SAID FILTER A FILTERED ELECTRICAL OUTPUT. 